The field of the invention generally pertains to light bulbs and lamps. The invention relates more particularly to a fluorescent bulb having a prophylactic sleeve surrounding a starter switch bulb which produces an electric discharge arc for initiating delivery of electric power through a fluorescent tube. The prophylactic sleeve helps reinforce and prevent the fluorescent bulb from breaking or otherwise malfunctioning when used with a work lamp in rough service applications.
Work lamps and shop lights have been developed for rough and rugged use by automotive mechanics, plumbers, technicians, etc. to durably and reliably light work areas. They commonly utilize fluorescent bulbs which must be sufficiently protected from impacts and other harsh jarring conditions which may cause the bulb to break or otherwise malfunction. Fluorescent bulbs typically include a light-emitting glass-tube connected to a base portion supporting a starter circuit. And the starter circuit typically comprises a heat sensitive switch encased in a secondary glass starter bulb.
Because the starter circuit functions to initially energize ionizable gas contained in the glass-tube for producing visible light, it is particularly important to keep it sheltered from harm. It is known, however, that the starter circuit, and particularly the glass starter bulb, is vulnerable to breakage or other damage from impacts caused by the relative movement of components disposed within the base portion, including the starter bulb. For example, because the starter bulb is typically suspended in the base portion only by flimsy wire conduits, the starter bulb may move and strike the inner surface of the base portion when subject to an impact. This vulnerability is aggravated when subject to rough service conditions of a demanding work environment.
Various measures have been developed to make fluorescent bulbs more durable by protecting, and thereby ensuring the proper operation of, the starter switch bulb. For example, in U.S. Pat. No. 5,675,941, a fluorescent lamp is disclosed having a hole along a base portion, through which an electrically and mechanically insulating material 150 is injected. As can be seen in FIG. 4xe2x80x2, the insulating material contacts a top portion of the glow starter switch, a portion of the fluorescent tube which extends into the base, and optionally a capacitor.
The arrangement of the ""941 patent, however, may allow a substantial portion of the starter bulb to be left exposed and unprotected (see FIG. 4xe2x80x2). Especially where moveable components are similarly disposed within the base of the fluorescent bulb, impacting contact with the starter bulb may be possible. Furthermore, notwithstanding the flexible nature of the injected compound, the cantilevered support arrangement at the top end of the starter bulb, as shown in FIG. 4xe2x80x2, may produce localized stresses in the starter bulb when, for example, the work lamp (and the fluorescent bulb) falls and strikes the floor in a lateral manner.
In summary, therefore, there is a need to provide a means for absorbing impacts against the starter bulb arising from the relative movement of components within the base cavity of a fluorescent bulb. In particular, padded protection of the sides of a starter bulb to impart a cushioning effect would be particularly advantageous due to the lateral direction of most impacts.
It is therefore an object of the present invention to provide an improved fluorescent bulb having a protective sleeve surrounding a starter switch bulb, wherein the protective sleeve is adapted to absorb impacts caused by relative movements of components held within a base portion of a fluorescent bulb, including the starter switch bulb.
The present invention is for an improved fluorescent bulb for use in a work lamp for rough service applications. The prior art fluorescent bulb is of a type having a fluorescent tube adapted to emit light when energized by electric power. The fluorescent tube is connected to a base portion having a base cavity, and a starter switch bulb is supported within the base cavity. The starter switch bulb is adapted to produce an electric arc for initiating delivery of electric power through the fluorescent tube. Additionally, the improved fluorescent bulb has a prophylactic sleeve surrounding the starter switch bulb, which is adapted to absorb impacts due to relative movements of components disposed within the base cavity, especially during rough service applications.